U.S. Pat. 5,542,685 having some inventors common with the above inventors and commonly assigned, includes a discussion of the technology of disks used in computer memory storage devices. Particularly, such patent discloses the problems attendant to the processing of the disks resulting in disk deformation and other damage caused by the handling and by the processing method and process apparatus. In that patent, a clamp or chuck is disclosed where a pair of clamping portions contact respective chamfered edges on a central disk aperture such that the disk is clamped by forces essentially acting traversely to a plane of the clamped disk. One of the clamping portions included a collet with collet segments being expandable to create a force against the chamfered edges at the disk ID. While this patent has been used commercially, the latest technology has required disks with improved smoothness and without substantially any deformation.
It has also been suggested by others that disk processing operations include processing and polishing the disk on both of its planar sides at the same time to save processing time and expense. However, it has been found that it is basically impossible to obtain a super smooth surface while polishing on both sides at the same time because as long as a polishing pad is in contact with a polished disk surface one will still see some marks, whether it is a polishing-induced mark, or a handling mark or a mark caused by the normal robot unloading of the disk from a carrier. Further, there normally are variations in the top and bottom polishing pads used so that the pad used for polishing one side of the disk is different from the pad used for polishing the opposite side of the disk. Also, since one disk side faces upwardly, contaminating particles can fall by gravity on the disk surface causing imperfections on that disk side. Also in the SpeedFam Inc. polisher devices currently employed by the disk manufacturing industry, the disks are mounted on a carrier thus being subject to scratches and deformation by contact with the carrier.
In general, equipment and processes as currently used, result in polished disk surfaces of about seven angstroms (7 .ANG.) in surface roughness. The term "super smooth" as used herein describes a desired surface roughness of less than three angstroms RMS. Particularly a surface roughness of only 2 .ANG. or 1 .ANG. is desired along with no significant change in disk flatness, i.e., no deformation of the disk. In the prior '685 patent directed to a device holding a disk at its internal diameter (ID), it was found that the pressure on the ID by the collet segments necessary to hold the disk, was such as to cause some disk deformation. This was particularly apparent in polishing aluminum disks and when the disks are vacuum-held in a carrier cavity on a polishing table of a disk polishing machine such as a SpeedFam polisher.
Others have approached the matter of disk smoothness by sequentially polishing the disk in a number of polishing machines using polishing slurries having finer and finer polishing particulates. The lost transfer time and the multiple sequential steps all increase the processing costs and limit yield. These costs are in addition to the capital costs of buying, operating and maintaining a multiplicity of polishing machines.